Methods for Determining the Nitrogen Fertiliser Requirements of Some Major Arable Crops

METHODS FOR DETERMINING THE NITROGEN FERTILISER REQUIREMENTS OF SOME MAJOR ARABLE CROPS IN FRANCE

Keywords: N fertiliser recommendations, balance-sheet method, nitrogen use efficiency, N status monitoring, decision support systems.

The paper provides an overview of the methods used in France to enable the calculation of forecast nitrogen (N) fertiliser recommendations, taking account of soil N availability and plant requirements. These methods, considered as frameworks, and some tools derived from the methods, require soil N measurements or/and plant measurements. The example of a tool based on the balance-sheet method (Azofert ^®) is emphasised. Plant measurements also enable more reliable predictions of plant N requirements to be made, as shown by a tool designed for oilseed-rape (‘Réglette colza’). Moreover, plant measurements based on N nutrition status in crops are used to monitor crops and to adjust fertilisation during crop growth in situations where nitrogen applications are split. In the last part, the authors discuss the use of the tools designed for decision-making, to help farmers to adjust fertilisation more accurately. They also highlight the necessary conditions for designing methods and tools for sustainable nitrogen management in the future.

V Parnaudeau^1,2, M H Jeuffroy³, J M Machet⁴, R Reau³, C Bissuel^1,2 and P Eveillard⁵.

¹ INRA, UMR1069 Sol Agro et hydrosystème Spatialisation, F-35000 Rennes, France.

² Agrocampus Ouest, UMR1069, Sol Agro et hydrosystème Spatialisation, F-35000 Rennes, France.

³ INRA, UMR 211 Agronomie INRA/AgroParisTech, BP 01, F-78850 Thiverval-Grignon, France.

⁴ INRA, US1158 Agro-Impact, Rue F. Christ, F-02000 Laon, France.

⁵ UNIFA, Le diamant A, F- 92909 Paris La Défense, France.

26 pages, 7 figures, 48 references.

DETERMINING NITROGEN FERTILISER REQUIREMENTS: THE DANISH NITROGEN PROGNOSIS SYSTEM

Keywords: Nitrogen, fertiliser, leaching, square grid, legislation, prognosis.

The nitrogen prognosis system is part of the nitrogen (N) legislation in Denmark. According to legislation the farmer must correct his N-quota for the N-prognosis every year. The nitrogen prognosis is a prediction of the difference between the demand for nitrogen fertiliser in the current year and the demand in a ‘normal’ year. Since 1987 sampling has been carried out for mineral nitrate in the Square Grid Net. The basis for the Danish nitrogen prognosis system is the Square Grid for Nitrate Investigations, which is a network of fixed measuring points at intervals of 7 km. Each measuring point covers an area of 2,500 m² and is at the intersection of a square grid with the side length of 7 km. A total of 830 points has been selected. 660 of these points cover arable land. The prognoses are based on measurement of mineral nitrogen to 1 metre depth in about 150 fields in the Square Grid Net and model calculations of another 150 fields.

Hans Spelling Østergaard, Danish Agricultural Advisory Service, Udkaersvej 15, Skejby, 8200 Aarhus N, Denmark.

13 pages, 5 figures, 2 tables, 5 references.

AN ASSESSMENT OF SOIL MINERAL NITROGEN AS A GUIDE TO THE NITROGEN FERTILISER RATE FOR WINTER WHEAT IN ENGLAND

Keywords: Soil mineral nitrogen, nitrogen response, winter wheat, nitrogen use efficiency.

TAG experiments in winter wheat funded by its farmer subscribers suggest that the use of measured soil mineral nitrogen as a precision diagnostic to estimate the optimum dose of applied nitrogen in individual fields has to be questioned. This is particularly in the context of the sites where these experiments were done. These represent typical arable situations in the UK where the long term cultivation of broad-acre crops has resulted in low soil organic matter levels and where there is no history of use of organic amendments or manures. In the 30 experiments in wheat grown after a range of combinable break crops, cereals and sugar beet, the soil mineral nitrogen measured in the spring varied from around 10 to just over 100 kg/ha. Despite this range of values there was no trend towards reductions in the economic optimum dose of applied nitrogen with increasing levels of measured soil mineral nitrogen.

Jim H Orson, TAG – The Arable Group, Morley Business Centre, Deopham Road, Morley, Wymondham, Norfolk, NR18 9DF, UK.

8 pages, 2 figures, 11 references.